1. Field of the Invention
The present invention relates to a technique for attaining high-speed color conversion of color image data.
2. Description of the Related Art
Application of an image display device, such as a color printer or a liquid crystal display unit, enables a color image to be displayed, based on color image data. Such image display devices are widely used as output devices of various image-related equipment like a computer.
The image display device combines a plurality of preset base colors to express a diversity of colors. The procedure for displaying a color image divides an original image into a plurality of small areas called pixels and expresses the colors in the respective pixels by combinations of the multiple base colors. Expression of the colors in the respective pixels leads to display a color image as a whole. The image display device receives a supply of color image data, which represents a mapping of the combination of tone values of the base colors to each pixel.
The base colors used for expression of color image data may be different from the base colors used by the image display device to display color images. In one example, the supplied color image data is expressed by combinations of three primary colors of light, that is, red (R), green (G), and blue (B), while the image display device uses combinations of three primary colors of ink, that is, cyan (C), magenta (M), and yellow (Y). In such cases, it is required to convert the color image data expressed by the tone values of the respective R, G, and B colors into another expression format based on the tone values of the respective C, M, and Y colors. Even when both the supplied color image data and the image display device use the combinations of R, G, and B colors for expression of a color image, there may be some difference in colors of R, G, and B between the color image data and the image display device. In such cases, in order to display an image of right colors, it is required to convert the master image data into image data expressed by the combinations of the R, G, and B colors used by the image display device. The process of converting master color image data into image data expressed by combinations of different base colors is generally referred to as color conversion. As mentioned above, the color image data is expressed by mapping the combination of tone values of the respective base colors to each pixel. The color conversion process thus converts the combination of tone values of original base colors into a combination of tone values of different base colors with regard to each pixel.
In such image display devices, with a view to displaying higher-quality images, the number of pixels per image tends to increase gradually. The increase in number of pixels allows division of an image into smaller areas for expression. This makes the respective pixels sufficiently inconspicuous and ensures expression of a higher-quality image.
The conventional color conversion process is carried out by the unit of a pixel. An increase in number of pixels thus undesirably lengthens the time required for color conversion of image data. The time-consuming color conversion makes it difficult to display a processed image within a short time.